latch free is a generic name for a latch problem. To find out the kind of problem we have to find out what latch the problem is on.
We can get information about "latch free" or any wait for that matter from V$EVENT_NAME. V$EVENT_NAME gives brief descriptions of the fields P1, P2 and P3 for a wait event:
In other words the latch# is P2 aka PARAMETER2. We can go int ASH and find out the id, the latch#, of all latch free waits we had:
In this case I was only getting waits on latch# 127. What is latch# 127? We can look it up in v$latchname:
Embarcadero's DB Optimizer does this for you (and OEM from Oracle doesn't)